Could be valve clearance but if you've got good compression I doubt it but worth a look.
If it tried to fire up once I'm with shadow fire you must have spark, of course it could have been the last gasp of a failing CDI or coil.
puropse
if you checked spark and you have none then my first suspect would be the CDI you can pick up a replacement for about $10 on amazon. next suspect would be the coil. not suggesting you start throw parts at it but
Those are cheap parts and even if the ones you have are good those are good spares to have laying around for the purpose of elimination.
Here is a decent article on trouble shooting the no spark condition.
http://www.buggydepot.com/tech-cente...uide-no-spark/
Good luck and keep us posted.